1. Field of the Invention
The present invention relates to a heat exchanger, and particularly to a series or stacked heat exchanger with a horizontally flowing charge air cooler and a vertically flowing jacket water cooler.
2. Description of the Related Art
It is well known that heat energy contained in one fluid is capable of being transferred to another fluid. Such heat transfer is described in the classical heat transfer equation: Q=UAdT. In this equation, Q represents the heat transfer, U represents a coefficient of heat transfer, A represents the surface area through which the heat can be transferred, and dT represents the change in temperatures between the two mediums. Heat exchangers, and radiators in particular, are designed for a relative high level of transfer of heat energy from one medium to another. One common example is an automobile radiator, in which a coolant fluid passes through an engine to absorb heat energy from the engine. The coolant fluid then is routed through the radiator, where heat is transferred from the coolant fluid to the environment (ambient air).
Engineers and designers have incorporated many strategies to increase the amount of heat that a heat exchanger is capable of transferring. One strategy is to attempt to increase the coefficient of heat transfer. Design components, such as the incorporation of louvers, dimples, waves, ridges and other alterations to the fin and tube profiles have been effectively used. While these improvements are quantifiable and generally useful, there are limitations (both practical and theoretical) as to how much the coefficient of heat transfer can be improved. For example, the increased capital investment in equipment and tooling costs may overshadow any savings associated with the increased coefficient. Accordingly, it may take a long time to recapture those costs through efficiency savings, if it is even possible at all.
Others have had success in increasing the heat transferring capability of the heat exchanger by increasing the surface area between the two mediums (i.e. increasing the size of the heat exchanger). The increases in surface area can come from a combination of increases in height, width, depth and density of the heat exchanger. Often times, the size requirements for shipping, packaging and deliverable use dictate maximum dimensions in the height and width dimensions. In such situations, the only remaining variable is the depth of the unit. Accordingly, designers have increased the depth of the heat exchanger in order to increase the surface area.
Some heat exchangers are designed for use with engines having turbochargers. It is standard practice to stack two or more radiators in series to cool both a jacket water coolant from the engine and charge air compressed by one or more turbochargers. The traditional configuration has a charge air cooler first, and a jacket water cooler second. Put another way, the charge air cooler is upstream of the jacket water cooler in some configurations, such that air first passes through the charge air cooler and second through the jacket water cooler. There are several drawbacks associated with the standard configuration.
It is well known that the maximum heat transfer in a charge air cooler occurs at the inlet side of the cooler where a maximum entering temperature differential exists between the fluids exchanging heat energy. The heat transfer decreases as the charge air passes through the cooler, as the temperature difference between the ambient air and the charge air decreases. The result is that the air (having passed through the charge air cooler) has an uneven temperature distribution as it passes through the jacket water cooler (the second cooler).
In a configuration where the charge air cooler has charge air moving up vertically through the cooler, the effective area of the jacket water cooler can decrease. This is because the air that passes through the charge air cooler near the inlet realizes the largest heat rise. The air with the largest heat rise can have a temperature that approaches or even surpasses the engine coolant temperature in the jacket water cooler. With little or no temperature differential in those areas of the jacket water cooler, no cooling takes place. The jacket water cooler can therefore operate at less than desired efficiency. To compensate for and overcome this inefficiency, air movers with increased horsepower capacity are utilized to move additional air through the heat exchanger. Yet, this approach can prove ineffective where little or no temperature differential exists. The standard configuration is therefore designed to be less than fully efficient.
A considerable amount of pressure, caused by the expansion of the air as it gains energy from the heat exchanger, can develop near the inlet sides of the coolers. This pressure gain can negatively affect the flow characteristics of the air passing through the coolers. The fan therefore needs to have greater horsepower capacity (i.e. higher initial cost plus increased energy consumption during operation) in order to move the intended amount of air through the heat exchanger at the desired locations to overcome the increase in external system pressure.
A further issue facing charge air coolers is the potential for axial thermal expansion of the tubes within the charge air cooler, which leads to local stress and high vibrations risk because of the different growth characteristics of the components of the heat exchanger.
A still further potential drawback associated with standard charge air coolers is that the inlet tube and header interfaces are subject to a great deal of stress. The weight of the charge air and the vibrations can exacerbate the stress at the joints.
Thus there exists a need for a heat exchanger that solves these and other problems.